The present invention relates to methods and compositions for use in subterranean operations. More particularly, the present invention relates to styrene-acrylate polymers used to treat tar resident in a well bore and associated methods of use.
Many subterranean operations involve the drilling of a well bore from the surface through rock and/or soil to penetrate a subterranean formation containing fluids that are desirable for production. In the course of drilling operations and other subterranean operations, the drillstring and/or other equipment may come into contact with zones of rock and/or soil containing tar (e.g., heavy hydrocarbons, asphalt, bitumens); in many such operations, it may be desirable to drill the well bore through these tar-containing zones. However, tar is a relatively tacky substance that may readily adhere to any surface that it contacts, including the surfaces of the well bore and/or any equipment utilized during the drilling operation. Tar also may dissolve into many synthetic treatment fluids used in the course of drilling operations, increasing the tacky and adhesive properties of the tar. If a sufficient amount of tar adheres to surfaces in the well bore or drilling equipment, it may, among other problems, prevent the drillstring from rotating, prevent fluid circulation, or otherwise impede the effectiveness of a drilling operation. In some cases, it may become necessary to remove and/or disassemble the drillstring in order to remove accretions of tar, a process which may create numerous cost and safety concerns. The accretion of tar on drilling equipment and/or in the well bore also can impede any subsequent operations downhole, including cementing, acidizing, fracturing, sand control, and remedial treatments. In addition, soft, tacky tar that manages to reach the surface may foul surface equipment, including solids screening equipment.
Existing methods of managing these problems that result from well bore tar incursion may be problematic. Some of these methods involve effecting an increase in hydrostatic pressure in the well bore so as to force the tar out of the well bore to the surface. However, this increased hydrostatic pressure may damage the well bore and/or a portion of the subterranean formation. Other conventional methods utilize treatment fluids that comprise dispersants, surfactants, and/or solubilizers, which allow the tar particles to dissolve in or homogenize with the treatment fluids. However, the tar particles may not be readily separated out of the fluid once they have dissolved into or homogenized with the fluid. The presence of the tar particles in the treatment fluid may alter its rheological properties and/or suspension capacity, which may limit its use in subsequent operations. Moreover, the addition of these dispersants, surfactants, and solubilizers may increase the complexity and cost of the drilling operation.